1. Field of the Invention
The invention relates to a testing system, more particularly to a system for testing electromagnetic characteristics of an electromagnetic steel sheet.
2. Description of the Related Art
FIG. 1 illustrates a conventional test system for electromagnetic characteristics of an electromagnetic steel sheet 103, i.e., a silicon steel sheet, based on a standard testing method defined by the American Society for Testing and Materials (ASTM).
The conventional test system includes a signal generating device 101 for generating a sinusoidal wave signal, and a linear power amplifier 102 coupled to the signal generating device 101 for receiving and amplifying the sinusoidal wave signal so as to output a voltage output that is applied across a first winding (N1) wound around the electromagnetic steel sheet 103 such that an exciting current flowing through the first winding (N1) is generated in response to the voltage output from the linear power amplifier 102, thereby resulting in an induced voltage across a second winding (N2) wound around the electromagnetic steel sheet 103. A wattmeter 104 and an oscilloscope 105 are used to measure the exciting current and the induced voltage. Thereafter, the electromagnetic characteristics of the electromagnetic steel sheet 103 in response to the sinusoidal wave signal can be obtained based on the exciting current and the induced voltage.
The electromagnetic steel sheet 103 is usually applied to a motor. A pulse width modulation (PWM) signal is used as a driving signal for the motor. As such, test result for the electromagnetic steel sheet 103 obtained by the conventional test system in response to the sinusoidal wave signal cannot exactly provide electromagnetic characteristics of the electromagnetic steel sheet 103 in response to a PWM signal when the electromagnetic steel sheet 103 is applied to a motor in actual use. In other words, if the signal generating device 101 generates a PWM signal rather than the sinusoidal wave signal, the PWM signal after amplifying by the linear power amplifier 102 has serious distortion. On the other hand, in another test system for an electromagnetic steel sheet with a specific specification in response to a PWM signal, a PWM amplifier is used. However, such PWM amplifier is not suitable for electromagnetic steel sheets with different specifications.